1. Field of the Invention
This invention relates to a communication system used in a semiconductor device manufacturing equipment.
2. Description of the Related Art
Generally, in a control unit for a semiconductor device manufacturing equipment, outputs of sensors or the like are supplied to the host computer, and information or data is transferred via a network to drive relays and solenoids or the like according to received data. In this case, a to-be-controlled system generally includes a plurality of slave side transmission systems and the slave side transmission systems are directly or indirectly connected to a master side transmission system to attain an interface between the transmission systems and the host computer. For communication between the master side transmission system and the slave side transmission systems, control sections such as microcomputers are provided in the respective systems and data transmission is effected by use of general interface, for example, transmission system RS232C which is widely used for serial transmission, for example. In the transmission system RS232C or the like, data is always transmitted in the unit of a character and synchronizing information items are inserted before and after the character. That is, the start bit is inserted before the character as the synchronizing information item and the stop bit is inserted after the character as the synchronizing information item.
In the above transmission system, it is necessary to set the start bit for each character and therefore the transmission speed becomes low. For example, with the general transmission system RS232C described above, the transmission speed is 9600 baud or 9600 bits/sec. For example, when all the 256-byte I/O data which can be managed by an 8-bit address is transmitted, at least one to several seconds are required for transmission, thereby causing a problem because high-speed transmission cannot be attained. Further, in the above transmission system, for example, if noise is imposed on data in the data transmission and the data disappears, disappearance of the data cannot be recognized on the receiver side and errors tend to occur, thereby sometimes lowering the reliability.
Further, as described before, it is necessary to provide an expensive integrated circuit such as a microprocessor not only in the master side transmission system but also in the slave side transmission system and the cost tends to become high.
In general, various types of sensors and driver systems are incorporated in various types of to-be-controlled devices, for example, semiconductor device manufacturing equipment, and in some cases, the operator wants to monitor the operating conditions thereof, but in the above system, the main computer of the network always monitors the status thereof via the interface, and when a display unit capable of displaying the ON/OFF state thereof by use of light emitting elements such as LEDs is provided in the computer, the monitoring process can be attained by operating the main computer.
However, if the main computer does not include such a display unit, the operating condition cannot be monitored. In this case, it is considered to interrupt the slave bus line on the slave side and monitor the operating condition, but since the input/output of the data line is controlled by the main computer, access cannot be freely made from the slave side.
Further, even if the main computer includes the above display unit, the operating condition of the to-be-controlled device cannot be monitored from the main computer side at the time of debugging of the slave side itself before the network is connected or when the network itself is down, for example.